Atoms — Physics STD 12 Science — Question

When the current changes from +2A to -2A in 0.05 second, an e.m.f. of 8V is induced in a coil. The coefficient of self-induction of the coil is:

Work of moderator is

(a) To control the velocity of neutrons	(b) Cooling
(c) As fuel	(d) It is used for safety

The speed of electromagnetic wave in vacuum depends upon the source of radiation

(a) Increases as we move from g-rays to radio waves

(b) Decreases as we move from g-rays to radio waves

(c) Is same for all of them

(d) None of these

An air capacitor of capacity C = 10μF is connected to a constant voltage battery of 12 V. Now the space between the plates is filled with a liquid of dielectric constant 5. The charge that flows now from battery to the capacitor is

(a) 120 μC

(b) 699 μC

(c) 480 μC

(d) 24 μC

Consider a region inside which there are various types of charges but the total charge is zero. At points outside the region:

A ball kept in a closed box moves in the box making collisions with the walls. The box is kept on a smooth surface. The velocity of the centre of mass:

1. Of the box remains constant.
2. Of the box plus the ball system remains constant.
3. Of the ball remains constant.
4. Of the ball relative to the box remains constant.

A wire of length 5 m and radius 1 mm has a resistance of 1 ohm. What length of the wire of the same material at the same temperature and of radius 2 mm will also have a resistance of 1 ohm

(a) 1.25 m

(b) 2.5 m

(c) 10 m

(d) 20 m